Known in Icelandic as Bláa lónið, the Blue Lagoon is Iceland’s most trumpeted geothermal spa, a surreal splash of colour and warmth amidst a bleak satanic wilderness of black lava rubble. It’s also a shameless tourist rip-off, though worth the price once for the experience: on cold days, when thick fog swirls over the warm, milky-blue water, your hair, dampened by vapour, freezes solid.

Blue Lagoon is actually artificial, dug into the middle of a flat expanse of black lava blocks and filled by outflow from the nearby Svartsengi thermal power station. Svartsengi taps into steam vents fed by sea water seeping down into subterranean hot pots, and by the time it emerges at Blue Lagoon it has cooled to a comfortable 38˚C. There are decoratively positioned caves and arches, a sauna, and the famous silvery-grey silt, said to cure skin disorders – Icelanders scoop handfuls off the bottom and smear it all over their bodies, and the shop sells beauty products made from it. Whatever the effects on your skin, hair takes a real battering from the lagoon’s enriched mineral content; rub conditioner in as protection before bathing.